Interpublic Group is considering taking a 95,000-square-foot commercial space at 100 W. 33rd St., where it already occupies some 400,000 square feet.

Interpublic Group is close to signing a lease for about 95,000 square feet at 100 W. 33rd St.

The company, one of the world's largest advertising and media conglomerates, is arranging to take the one million-square-foot building's entire fourth floor in a 15-year deal for rents of about $50 per square foot.

The lease will be an expansion for the Big Four advertising firm, which already occupies about 400,000 square feet at the 13-story property.

Interpublic will move several subsidiaries into the new space, though it was not immediately clear by press time which groups would fill the new floor.

The lease is the second sizable transaction completed in recent months between the company and Vornado Realty Trust, the large real estate investment trust that owns 100 W. 33rd St.

In October, Vornado completed a 220,000-square-foot lease to bring Interpublic to another office tower it owns, 909 Third Ave., in what so far has been one of the largest leases signed in a slow second half of the year. In that transaction, several Interpublic subsidiaries, including public relations giant Weber Shandwick, agreed to move to the tower from nearby 919 Third Ave., which is owned by the rival real estate investment trust SL Green Realty Corp.

A source said Interpublic will now have about 750,000 square feet between the two Vornado buildings.

Scott Panzer, a broker with Jones Lang LaSalle, represented Interpublic in the deal at 100 W. 33rd St. Glen Weiss, an in-house leasing executive at Vornado, helped arrange the leases with the company at both 909 Third Ave. and 100 W. 33rd St.

Interpublic will take possession of the West 33rd Street space in late 2013. The fourth floor was formerly occupied by Bank of America Corp., which vacated the building last year.

The expansion deal with Interpublic may not be the only transaction pending at 100 W. 33rd St. The apparel tenant Aéropostale, which bases its offices at the tower, is said by several sources to be considering a renewal and possible expansion at the property. The company currently has about 100,000 square feet at the building, and its leases expire in 2015 and 2016.